1. Field of the Invention
The invention relates to a cyanine dye which is suitable for use as a .lambda.=450 nm -650 nm visible light-absorbing organic dye such as DVD-R.
2. Description of the Related Art
A storage medium with higher storage density, smaller size and lower cost is extremely required now-a-days. As magnetic storage medium is not able to satisfy these requirement, optical storage material is greatly sought for as an alternative. It is found that organic dye which combines the advantages and characters of both the photosensitizer and photorecording medium, is highly developed and adopted for optoelectronic industry. The applications of organic dye include in the fields of, for example, nonlinear optical device, recording and displaying of optical disc data, photoresist, sensor and indicator for heat, light, and electron, during the transfer and storage of energy, medicine and biology, etc. The cyanine dyes mixture of this invention has high absorption coefficient in the infrared region which implies that the cyanine dye has high recording sensitivity and signal to noise ratio (S/N) value. Therefore, cyanine dyes mixture is an ideal optical memory storage material.
An organic dye, cyanine blue, was first synthesized by Greville Williams in 1856 (K. Venkataraman (ed.), The Chemistry of Synthetic Dyes, Vol. II, p.1143-1186, Acdaemic Press, New York, 1952.). In 1875, Vogel discovered that Cyanine Blue has special photosensitive properties. Therefore, cyanine blue, which was originally used as colorant turned to be a photosensitizer with higher added value. Different structures of cyanine dye have different .lambda..sub.max which varies from UV to IR. Therefore, cyanine blue can also serve as photosensitizer for photoresist or optical storage medium in electronic industry besides a colorant.
Cyanine dye, 3, 3'-diethyl-12-acetyl-thiatetracyanine perchlorate, was first proposed for the application in optical discs fabrication by Law et al. Discusser that (K. Y. Law, P.S. Vincett, and G. E. Johnson, Appl.Phys.Lett., 39, 718(1981)). The cyanine dye and PVAc (poly(vinyl acetate)) are first mixed and then spin-coated to form an optical recording medium. After this successful application, several kinds of cyanine were develop for optical disc applications, such as those disclosed in U.S. Pat. Nos. 5,019,476, 5,292,615, 5,328,802, 5,332,608, 5,424,171, 5,455,094 etc. As to the method of fabrication, it is found that spin coating of the dye on the substrate can shorted the process and reduce the cost as compared to the chemical vapor deposition (CVD) process; therefore spin coating is accepted as the standard procedure, and the stability if the organic dye and its solubility to organic solvent are critical factors for successful applications.